Question (3) (35 marks): a) Draw 3-bit down ripple counter using two implementations one of them by using D FFs. (10 marks) b) Design a counter with RS flip-flops that goes through the following binary repeated sequence: 0,1,3,7,6,4. (10 marks) c) Design a four-bit (A,B,C,D) combinational circuit 2's complementer (the ou generates the 2's complement of the input binary number). Show the circ constructed with XOR gates. (15 marks)